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The selection of materials for wear parts in oxygen pumps or compressors is critical from an oxygen compatibility perspective because the function of the part is to absorb frictional energy. Part of this energy is absorbed by the sample as heat and can cause ignition of the material. There is little data on the compatibility of bronze alloys typically used for wear parts in oxygen systems, so it is difficult to ensure that the most compatible materials are used.
This paper discusses frictional heating test data obtained for seven bronze alloys which could be used in certain applications as wear parts. A test apparatus developed by the NASA test facility at White Sands to determine the resistance of materials to ignition by friction was used to obtain the data. The bronzes evaluated were selected based on the ability to function mechanically in the intended application and the anticipated resistance to ignition by friction. The alloys were ranked according to the resulting pressure-velocity (PV) product. This factor serves as a measure of the load required for ignition given a constant sample load rate, a constant gaseous oxygen pressure, and a constant sample rotational velocity. Factors influencing the test results including sample composition, material properties, and test procedures are addressed. A simple theoretical description of the phenomenon of ignition by friction is presented to explain the effects that the proposed variables may have on the PV product.
bronze alloys, friction, ignition, frictional heating test, wear ring, liquid oxygen pump
Materials Engineer, National Aeronautics and Space Administration, John C. Stennis Space Center, MS